You can buy packs and funds using coins or you can watch videos to earn them.

To access these videos go to Shop menu, then tap Resources. You can also access this page if you click on a packs or the funds icon at the upper side of your screen.

Note that these videos are not available all the time, so if you do not see them please be patient.
Always make sure to have a stable connection before watching videos. If the videos get interrupted due to poor connection you might miss the reward.